Will it be cigarettes: none; alcohol units: none; weight: off the charts; baby: imminent, as Bridget Jones returns for a "different phase" of London life?

Author Helen Fielding announced this morning that she is writing a third novel about Britain's favourite singleton, Bridget, due out next autumn – 13 years after Bridget last appeared between the pages of a novel. Publisher Jonathan Cape would only reveal that the novel "explores a different phase in Bridget's life", refusing to say if Bridget's perennial paramours, Mark Darcy and Daniel Cleaver, would make an appearance in the story, or if Bridget would have aged in real time, making her at least in her late 40s.

"The new novel is set in present-day London, with an entirely new scenario for Bridget," said Fielding. "If people laugh as much reading it as I am while writing it then we'll all be very happy."

Speaking on Woman's Hour this morning, Fielding admitted that Bridget's famous diary style – she opens each entry with a list: "9st 3 (but post-Christmas), alcohol units 14 (but effectively covers 2 days as 4 hours of party was on New Year's Day), cigarettes 22, calories 5424)" – would be focusing more on Twitter followers than on alcohol and cigarettes this time around. "It's more like 'number of Twitter followers: 0. Still no followers. Still no followers'. But she has grownup. My life has moved on and hers will move on too," said Fielding. "She's still trying to give up [drinking and smoking], she's still on a diet. She's trying a bit harder, and is a bit more successful, but she's never really going to change."

Fielding, who is also working on a third Bridget Jones film which is not based on a novel as well as a Bridget Jones musical, said she had become interested in internet dating, specifically those "cyber presences who aren't real, half of them", and "how people can have entire relationships by text which in some ways are emotionally fulfilling".

"In the same way as the first Bridget book was looking at the way a 30-something single woman was branded as a tragic spinster, and then we got the new idea of a singleton, [the new book] will be looking at later phases in life when you get branded as a certain thing," she said, "and you don't have to be that at all and it's all outdated and ridiculous. I'm having a lot of fun and it's very funny and it's making me laugh. It's a bit scary bringing out another one but I'm really enjoying writing it."

As to what's happened to Darcy and Cleaver, she revealed very little. "Some characters remain and some may have disappeared," she said. "They'll still be presences in the book. Like all of us you keep your friends, people stay in your life, but everyone's life moves on."

Bridget Jones started out as a column in the Independent in 1995, following the life of a 30-something singleton in London. The first novel, Bridget Jones's Diary, was published in 1996 and is often credited with launching the chick lit phenomenon. It saw Bridget recount the minutiae of her life, weight changes and romantic pitfalls, as she vacillated between the men in her life, good but dull Mark Darcy, and wrong but romantic Daniel Cleaver. Bridget Jones: The Edge of Reason, was published in 1999, and continued the theme – although Bridget starts out happily shacked up with Mark, a trip to Thailand sees Daniel back on the scene. Together, the novels have sold over 15m copies worldwide, helped by film adaptations starring Renée Zellweger, Hugh Grant and Colin Firth in 2001 and 2004.

The novelist India Knight, who "loved" the first Bridget Jones but was less keen on the "mad" second one, said she hoped Fielding would be ageing Jones in real time, making her now in her late 40s or early 50s.

"It would be great to have commercial women's fiction narrated by somebody older," she said. "I'm really curious about it … I love the idea of Bridget Jones, broken and lonely two divorces later, with a bottle of red wine, blogging insanely ... I'd like to see her with troublesome teenage children, but the timing probably wouldn't work out. So I'd like to see her as a much older mother. I'd like more darkness. [Fielding is] such a good comic writer, she would do it so well, make it bittersweet, dark but funny. I hope Bridget's not some awful giddy cougar but I think that's unlikely."

Although Cape would not reveal any more details about Bridget's new adventures, online speculation was quick to wonder if she would be discovering online dating, or blogging rather than writing a diary.

The Cape publisher Dan Franklin hailed Fielding as a "great comic writer" who has created a character "of whom the very thought makes you smile", but remained tight-lipped on the contents of her new adventures.

"Like millions of others I can't wait to see what's happened to her," he said.